1. Field of the Invention
The present invention relates to a seal assembly and, more particularly, to an improved seal assembly for minimizing fluid leakage in a hydraulic hand tool.
2. Brief Description of Prior Developments
Hydraulic powered hand tools are commonly used in manufacturing, industrial, and maintenance sites and facilities. These tools include drivers for bolts, nuts, screws and like fasteners. In these settings it is often critical that particular fasteners be installed with a predetermined amount of torque at high torque values.
With the demand for increasingly high power and torque settings required for various applications, the current seals surrounding a drive shaft and contacting a motor housing of these hydraulic powered hand tools are limited in life. The current seals, such as the seal disclosed in U.S. Pat. No. 3,738,665, or the lip seal used in current BURNDY® hydraulic tools, produce shaft wear. Although the seal has a much lower hardness than the hardened steel shaft, under temperature and elevated hydraulic pressure, the seal is abrasive to the steel and causes wear rings to be formed. At high speeds/temperatures/pressures, these wear clearances are nominal because the parts are expanded. However, once the tool sets for a few hours, the clearance between the seal and the shaft becomes more pronounced. Worn seals between the hand tool housing and the shaft have been a known problem that results in fluid leakage from the motor. The seal disclosed in U.S. Pat. No. 3,738,665 utilizes a hard (inflexible) steel carrier ring having an inner and an outer seal. The inner seal is expanded by o-ring, and the entire seal assembly is compressed under hydraulic load. This results in non-uniform sealing pressure which promotes shaft and seal wear. The seals may further exhibit distortion and result in unacceptable clearances minimizing the effectiveness of the seal.
Therefore, there is a need for a seal assembly which provides a substantially uniform sealing pressure against the shaft and the housing when the tool is hydraulically loaded and when the tool is at rest. This uniform sealing pressure reduces wear, minimizes leakage and promotes increased service life of the seal assembly.